Infundibular widening of cerebral arteries can develop into true aneurysms. Mid-term and long-term follow-up MRI (e.g., in yearly intervals) is advised for infundibula with a diameter of 3 mm or more. In patients with other aneurysm(s), with a documented de novo aneurysm formation or with a familial occurrence of aneurysms, the risk of evolution of an infundibulum to a saccular aneurysm may be increased and follow-up should be even more stringent.